What exhaust cam control does
On engines with a variable exhaust cam, an oil-pressure actuator moves the cam relative to the crank, and a solenoid pulsed by the ECU controls that oil flow. The Nexus compares the measured cam angle with your target and adjusts the solenoid duty until they match. It's the same closed loop idea as intake cam control, applied to the exhaust side. Moving the exhaust cam changes overlap with the intake, which affects idle quality, spool, emissions and where the engine makes its power.
The main settings
| Setting | What it does | Our advice |
|---|---|---|
| Exhaust Frequency | How fast the solenoid is pulsed | Lower frequencies give a wider usable duty range but can make the solenoid rattle; higher ones narrow the usable range. Start from the base map or factory value |
| Exhaust Duty Cycle Min | Lowest duty the controller may command | Set it just where the solenoid starts to respond, so the controller doesn't waste time in the dead zone |
| Exhaust Duty Cycle Max | Highest duty the controller may command | Set it where extra duty stops making a difference |
| Exhaust Cam Direction | Which way the controller drives the cam | Exhaust cams are normally set to Retard |
| Enable Exhaust Overall Corr | Adds an Overall Correction table on top of the target | Handy for quick experiments on the dyno |
Target angle table
This is the table that actually sets exhaust cam timing, in up to 4D. A common shape is more retard at very low RPM, less through the midrange, and a bit more again near redline, but the right numbers only come from dyno testing on your engine. We sweep the cam at a few load points and keep the angle that makes the most torque, while watching exhaust temperature and, on turbo engines, spool. If you're scaling targets with another input, see Target Scalar.
Base duty cycle: the step most people skip
The base duty table (up to 3D) holds the duty needed to hold the cam at its target once it's there. If this table is right, the PID controller only has to handle small corrections, and the cam moves quickly without overshooting. Here's how we find it:
- Hold the engine steady somewhere around 2000 to 3000 RPM, so oil pressure is fully up.
- Command a target angle that isn't zero.
- Watch the Cam Control Exhaust Bank 1 (or Bank 2) output channel.
- Once the cam has reached the target and settled, note the duty the controller is using.
- Enter that value into the matching Exhaust Base Duty Cycle table.
If base duty is too low, the cam is slow to reach its target. If it's too high, the cam overshoots and hunts.
PID tuning
The PID tables (each up to 3D) set how aggressively the controller chases the target. Proportional responds to how far the cam is from target. Integral works on the error that remains over time. Derivative damps the response so an aggressive proportional term doesn't overshoot. As a rough starting point for cam control, integral is often about half the proportional value, with a small amount of derivative to stop overshoot. From there it's testing: step the target and watch how the cam responds in the log. Our guide to PID control mapping goes deeper.
Overall correction and long term trim
With Overall Correction enabled, you get a single table that shifts the exhaust target up or down without editing the main table. It's great for trying ideas quickly; just fold the result back into the target table when you're done.
Long term trim learns how the solenoid really behaves over time and stores corrections in its own table:
- Long Term Trim Gain (up to 3D) sets how quickly it learns. Higher values learn faster but can cause oscillation; lower values are slower and steadier.
- Long Term Trim table (up to 3D) shows the corrections it has learned. You can set its breakpoints, but it always uses the same axis channels as the base duty table. You can also edit it yourself while learning is running.
Troubleshooting
| Symptom | Usually |
|---|---|
| Cam overshoots, then settles | Base duty too high, or proportional gain too high with too little derivative |
| Cam is slow to reach target | Base duty too low, gains too soft, or low oil pressure |
| Cam moves the wrong way | Cam direction setting is wrong |
| Solenoid buzzes or rattles | Frequency too low for this solenoid |
| Cam doesn't move at all | Check the cam control wiring, output assignment and duty limits |
For the overall cam setup, including cam sensor configuration, start with the main Cam Control article.
